This invention relates to multiple pole coupling discs of the type used in an electromagnetic coupling such as an electromagnetic clutch or brake. The coupling disc may be part of a rotary or non-rotary field or may be a rotary or non-rotary armature.
A typical electromagnetic coupling is disclosed in Silvestrini et al U.S. Pat. No. 4,187,939 and, in that particular case, the coupling is an electromagnetic clutch having a rotary armature disc made of material having low magnetic reluctance such as steel and having a field with a rotor which also is made of steel. When the coil of the field is excited, magnetic flux threads a path between the rotor and the axially opposing armature and attracts the armature into engagement with the working face of the rotor to couple the two for rotation in unison. The working face of the rotor is defined by one face of a disc which forms part of the rotor.
The coupling disc of the present invention is particularly useful in conjunction with a rotor which is used, for example, in the clutch of a vehicular air conditioning compressor. A pulley is attached to an outer pole ring of the rotor and is driven by an endless belt. When the clutch is engaged, the rotor is subjected to relatively heavy belt loads.
Rotors which are particularly useful with the clutches of air conditioner compressors are disclosed in detail in Booth et al U.S. Pat. No. 4,685,202; Roll et al U.S. Pat. No. 4,891,077; Booth et al U.S. Pat. No. 4,891,619; Booth et al U.S. Pat. No. 4,951,797; Booth et al U.S. Pat. No. 5,096,036 and Brown et al U.S. Pat. No. 5,125,255. The rotors disclosed in those patents have comparative advantages and disadvantages but, in a general sense, they share a common disadvantage. That is to say, such rotors are generally not suitable for use when in the form of a relatively small diameter rotor which must be capable of carrying heavy belt loads without failing structurally, which must be comparatively light in weight and which, at the same time, must possess acceptable magnetic characteristics. For the most part, the rotors disclosed in the above patents include coupling discs formed with radially spaced rows of angularly spaced "banana" slots which are separated by relatively narrow webs or bridges. If the rotor disc is of relatively small diameter and is thin in an axial direction, the webs eventually bend under heavy belt loads and lead to structural failure of the rotor.